This invention concerns a method and apparatus for inexpensively and effectively cathodically protecting reinforcing members in reinforced concrete structures. In particular, the invention concerns an anode structure comprising an electrically conducting tape disposed on a electrically insulating backing. The backing is directly applied to a concrete structure and the tape and backing are held in place by an overlying, electrically conducting coating that completes the structure.
The corrosion of reinforcing members, which are ordinarily made of steel, in reinforced concrete structures such as bridge piers, decks and railings, parking garage floors, etc., is a constant problem. In climates where snow and ice accumulate, the brine produced by ice-melting salts induces and accelerates the corrosion problem. Salt-accelerated corrosion is also encountered in coastal areas where salt water contacts reinforced concrete structures. Chloride ions accelerate the corrosion of steel reinforcing members and help generate corrosion products that occupy a larger volume than the uncorroded steel. The corrosion products create severe internal pressure on the concrete resulting in cracking and spalling. Once cracking and spalling begin, access to reinforcing members increases, further accelerating the rate of corrosion, cracking and spalling.
Cathodic protection is a well known and effective method of combating corrosion in reinforced concrete structures. In cathodic protection, a small electrical current supplied by an external direct current power source flows from an anode disposed on the surface of the concrete to the reinforcing members within the concrete structure which act as a cathode. This current flow counteracts the electrical current that would flow in the course of electrochemical corrosion of the reinforcing members and inhibits the electrochemical corrosion reaction. The negative sense terminal of the external power supply is connected to the reinforced structure by exposing a reinforcing member at one or more locations so that the necessary electrical connections can be made. The openings are then covered with fresh concrete, grout or another material to protect the reinforcing members.
A number of techniques for making anode connections to reinforced concrete structures are known. A typical connection is disclosed in U.S. Pat. No. 4,255,241 to Kroon et al. for "Cathodic Protection Apparatus And Method For Steel Reinforced Concrete Structures". There, an anode is formed in a slot sawn into the concrete structure. An insulator is disposed on the innermost surface of the slot. The slot is then filled with an electrically conducting material in which is suspended a platinized niobium wire. The remainder of the slot is filled with an inert material so that a surface flush with the original surface of the concrete is formed.
Known anode structures, like those disclosed by Kroon, require an expensive platinized niobium wire. The installation process for those anode structures requires a significant amount of expensive labor. Accordingly it is desirable that a cathodic protection system for reinforced concrete structures employ an anode structure that is inexpensive both in materials cost and the cost of installation.